Fuel flow control apparatus for gas turbine engines



Sept. 3, 1968 o. N. LAWRENCE 3,399,530

FUEL FLOW CONTROL APPARATUS FOR GAS TURB INE ENGINES Filed March 17, 1967 United States Patent 3,399,530 FUEL FLOW CONTROL APPARATUS FOR GAS TURBINE ENGINES Owen Napier Lawrence, London, England, assignor to Joseph Lucas (Industries) Limited, Birmingham,

England, a British company Filed Mar. 17, 1967, Ser. No. 624,015 1 Claim. (Cl. 6039.28)

ABSTRACT OF THE DISCLOSURE A fuel supply system for a gas turbine engine having a throttle controlled by a servopiston by means of a manually controlled plunger, the servopiston being disposed in a cylinder to one end of which fuel is supplied through a restricted passage, there being a passage for escape from end in dependence upon the position of the plunger, there being a further passage affording communication between the cylinder and a further cylinder containing a piston having a restricted by-pass and a member operable with the manually controlled plunger to cause the piston to move if the speed or extent of travel of the plunger and member exceed a value corresponding to the rate of flow capable of taking place through the restricted by-pass, thus delivering fuel to the cylinder to move the piston at a rate in excess of that possible by flow through the first mentioned passage thereto.

This invention relates to fuel flow control apparatus for gas turbine engines and is intended to control additional supplies of fuel for acceleration purposes. Such apparatus is described in the provisional specification of co-pending British patent application No. 39,526/ 65.

The object of the present invention is to provide apparatus of the kind referred to in a convenient form whereby the supply of additional fuel for acceleration purposes is related to the rate of acceleration required.

In accordance with the present invention apparatus for controlling the supply of fuel to a gas turbine engine comprises a pump, an axially movable throttle in a duct between the pump and the engine, a piston in a cylinder, said piston being connected to the throttle, one end of the cylinder being in use, supplied with fuel through a restricted passage from the upstream side of the throttle, a manually operable plunger movable coaxially within the piston, relative axial movement between the plunger and the piston controlling the escape of fuel from said one end of the cylinder, a passage affording communication between said one end of the cylinder and a further cylinder at one end thereof, said further cylinder containing a piston and there being a restricted bypass between the ends of the further cylinder at opposite sides of the piston therein, and means arranged to extend into the end of said further cylinder remote from that with which the passage communicates, said means being operable in response to movement of the manually operable plunger, for tending to cause flow through said restricted by-pass, when the plunger is moved to initiate acceleration of the engine, by cutting off or reducing the escape of fuel from the first mentioned cylinder, the arrangement being such that, in the event that movement of the manually operable plunger to accelerate the engine tends to cause a greater flow through said by-pass than it can accommodate, the further piston will move to deliver fuel to the first mentioned cylinder to move its piston, and thus the throttle, at a greater rate than can be achieved by flow of fuel to said first mentioned cylinder through said restricted passage.

The invention will now be described with reference to the accompanying drawing, the single figure of which is Patented Sept. 3, 1968 a diagrammatic view of apparatus for controlling the flow of fuel to a gas turbine engine.

The apparatus includes a pump 5 controlled by an hydraulic piston and cylinder type servo 6 and arranged to obtain a supply of fuel from a reservoir (not shown) through a boost pump 7. Fuel flow to the engine is controlled by a throttle 10 slidably mounted in a suitable body 8 to which the pump 5 supplies fuel through a supply duct 11 and there is an outlet duct 12 to burners 9 in the engine, there being a pressurising valve 13 in the outlet duct 12. The throttle 10 is of the kind comprising a rod-like member which is fluted at its free end, this fluted end being disposed adjacent to an annulus 14, the position of the throttle 10 in relation to the annulus 14 determining the rate of flow of fuel to the engine. Across the throttle 10 is provided a means for maintaining a constant pressure drop, this means being indicated at 15, and having a diaphragm 15a to opposite sides of which fuel is admitted from upstream and downstream sides of the throttle 10 respectively. The position of the diaphragm determines the position of a lever 15b carrying a valve closure member which controls flow of fuel to the servo 6 of the pump 5 in order to regulate the output of the pump 5.

The position of the lever 15b is however also influenced by a capsule assembly 150 which is responsive to charges in air pressure conditions existing within the compressor stage of the associated gas turbine engine.

The pressure acting upon one side of the diaphragm 15a is moreover modified in accordance with a device 16 which is responsive to temperature conditions obtaining within the engine, this device 16 being of substantially conventional form.

The throttle 10 has a tubular extension 10a terminating in a piston 17 which is disposed in a cylinder 18, to the end of which adjacent to the throttle 10, fuel is normally supplied through a passage 19, incorporating restrictors 20, from the supply duct 11 at the upstream side of the throttle 10. The tubular extension 10a has an orifice 21 in its wall, this orifice normally being disposed in that part of the tubular extension within the cylinder 18, and being capable of registering with a transverse passage 22 in a plunger 23 which is manually operated by the pilot, in the case of a fuel system fitted to an aircraft. Such manual operation is by means of a rack and pinion 24 and a lever 25. The transverse passage 22 in the plunger 23 communicates with a longitudinal bore 26 in the plunger 23 which is in communication with a further orifice 27 at or near the junction of the tubular extension 10a with the throttle 10, this orifice 27 communicating, through a gallery in the body 8 and a passage 28, with the inlet of the pump 5, or other relatively low pressure portion of the system.

The opposite end of the cylinder 18 is in communication through restricted passages 29, 30 with the upstream and downstream sides of the throttle 10, the passage 30 being restricted at opposite sides of its junction with the passage 29.

The apparatus thus far described in substantially that which is described in the provisional specification of our copending British patent application No. 39,526/65, and operates in the following manner. In the event of the pilot wishing to accelerate the engine from one speed to a higher speed, the plunger 23 is moved to the right, as viewed in the drawing, thus cutting communication between the orifice 21 and the transverse passage 22 in the plunger 23, so as to prevent escape of fuel from the end of the cylinder 18 to the passage 28. Assuming that the travel is relatively short, or alternatively that it takes place relatively slowly, the pressure will be built up in the end of the cylinder 18 by the flow of fuel through the passage 19 and through the restrictors 20, thus moving the piston 17 to the right until the orifice 21 again registers with the transverse passage 22, thus enabling equilibrium conditions to be regained with the throttle in a new position with respect to the annulus 14, so that an increased rate of flow of fuel can reach the engine.

If however the travel of the plunger 23 is large, or alternatively is performed relatively quickly, there arises the condition in which the restrictor will prevent the inflow of fuel to the cylinder 18 at a rate which will move the piston 17 and thus the throttle 10 at a desired speed for rapid acceleration. Under these circumstances additional fuel is supplied through a passage 32 to the cylinder 18.

Such fuel reaches the cylinder 18 through the passage 32 from a further cylinder 33. The cylinder 33 is supplied with fuel from the inlet duct 11 through a restricted passage 31, the passages 31 and 32 communicating with the further cylinder 33 at the same side of a piston 34. This piston 34 is urged by a spring 35 into engagement with a fixed abutment 36.

The passages 31, 32 communicate with that end of the cylinder 33 in which the spring 35 is housed, and the piston 34 incorporates a restricted by-pass orifice 37, through which fuel can flow between opposite sides of that piston 34.

The end of the further cylinder 33 containing the fixed abutment 36 also has a plunger 38 which is engageable by the pinion of the rack and pinion 24, through a further rack 39 on this plunger. Movement of the plunger 38 into the cylinder 33 which occurs in unison with movement of the plunger 23, in a direction to cause acceleration of the engine, reduces the volume of that end of the further cylinder 33 into which the plunger 38 protrudes, and if the movement is small or alternatively, if the movement is relatively slow, the restricted orifice 37 in the further piston 34 will accommodate the flow of fuel thus caused without movement of the piston 34.

If however the movement of the plunger 38 as well as the movement of the plunger 23 is great and/or relatively rapid, the restricted orifice 37 is incapable of accommodating the necessary flow, thus causing the piston 34 to move against its spring 35 and this will have the effect of closing the passage 31 and forcing some of the fuel in the cylinder 33 through the passage 32 and into the cylinder 18, to move the piston 17 more rapidly than can otherwise be achieved through flow through the restricted passage 19.

As the pressure drop across the further piston 34 decreases, and the flow through the restricted orifice 37 becomes adequate to enable the piston 34 to move under the action of its spring 35 to re-open the passage 31, so that the flow to the cylinder 18 through the passage 32 ceases, and the speed of movement of the piston 17 decreases, and eventually ceases, when the orifice 21 registers with the transverse passage 22 in the plunger 23, thus re-establishing equilibrium conditions.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. Apparatus for controlling the supply of fuel to a gas turbine engine comprising a pump, an axially movable throttle in a duct between the pump and the engine, a piston in a cylinder said piston being connected to the throttle, one end of the cylinder being in use, supplied with fuel through a restricted passage from the upstream side of the throttle, a manually operable plunger movable coaxially within the piston, relative axial movement between the plunger and the piston controlling the escape of fuel from said one end of the cylinder, a passage affording communication between said one end of the cylinder and a further cylinder at one end thereof, said further cylinder containing a piston and there being a restricted by-pass between the ends of the further cylinder at opposite sides of the piston therein, and means arranged to extend into the end of said further cylinder remote from that with which the passage communicates, said means being operable in response to movement of the manually operable plunger, for tending to cause fiow through said restricted by-pass, when the plunger is moved to initiate acceleration of the engine, by cutting off or reducing the escape of fuel from the first mentioned cylinder, the arrangement being such that, in the event that movement of the manually operable plunger to accelerate the engine tends to cause a greater flow through said bypass than it can accommodate, the further piston will move to deliver fuel to the first mentioned cylinder to move its piston, and thus the throttle, at a greater rate than can be achieved by flow of fuel to said first mentioned cylinder through said restricted passage.

References Cited UNITED STATES PATENTS 2,621,632 12/1952 Ifield 9l48 2,685,334 8/1954 Davies -39.28 XR 3,173,468 3/1965 McCombs 60-3928 XR JULIUS E. WEST, Primary Examiner. 

